A Schottky barrier diode (i.e., SBD) includes a Schottky electrode, which contacts a semiconductor layer. An interface between the Schottky electrode and the semiconductor layer has a small work function between metallic material composing the Schottky electrode and semiconductor material composing the semiconductor layer. Accordingly, when a reverse voltage is applied to the diode, a leak current in the SBD is larger than a PN junction type diode.
JP-2000-294804 discloses a construction having a Schottky junction and a PN diode. Specifically, the PN diode is formed in a part of the Schottky junction, so that a leak current is reduced when a reverse voltage is applied to the construction. More specifically, as shown in FIG. 11, a Schottky electrode J1 and a N− type drift layer J2 contact with each other at a contact region, which is disposed on an inner side of a RESURF layer J3. The RESURF layer J3 provides a terminal region (i.e., outer periphery breakdown region). A P type layer J4 disposed in a surface portion of the drift layer J2 has a stripe pattern. The P type layer J4 is disposed in the contact region so that the PN diode is formed in the part of the Schottky junction.
However, since the P type layer J4 has the same depth as the RESURF layer J3, a depletion layer expands with an edge shown as a dotted line in FIG. 11 when surge occurs in the device. Thus, the depletion layer approaches the N− type layer J2. Accordingly, electric field is easily concentrated at a portion XI, which is a boundary between the N− type layer J2 and the RESURF layer J3, thereby, the device is easily broken down.
Thus, it is required for the SiC semiconductor device having a JBS (i.e., junction barrier Schottky) diode to protect from breakdown caused by electric field concentration when the surge occurs.